Reading and the Posterior Parietal Cortex: A tDCS Study
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1
Australian National University, Australia
Aims: The dorsal visual pathway has been implicated in reading; specifically, in the sequential allocation of spatial attention to letters within words. An “attentional spotlight” is hypothesised to assist in detecting letters prior to further processing. This study aimed to test the attentional spotlight hypothesis using transcranial direct current stimulation (tDCS) over the right posterior parietal cortex (rPPC), part of the dorsal pathway. It was predicted that anodal stimulation would reduce reaction time in a word recognition task, particularly for stimuli with altered spatial properties. Cathodal stimulation was predicted to increase reaction time, especially for spatially altered stimuli.
Method: Participants completed a lexical decision task (LDT) involving normal and spatially displaced word stimuli while undergoing tDCS. All participants underwent cathodal, anodal and sham (control) stimulation in separate sessions.
Results: Analysis of the three sessions showed that stimulation had different effects on separate testing occasions. In Session 1, responses under anodal stimulation were significantly slower than sham for one in six stimulus types (p = .023). In Session 3, task reaction times for anodal stimulation were significantly faster than sham for all stimulus types (p = .01). Spatially altered stimuli were affected relatively more than their typically presented counterparts for one in three cases in Session 3 (p < .05).
Conclusions: The reversal of effects between Sessions 1 and 3 can be accounted for by learning processes. In Session 1, anodal stimulation inhibited learning of the LDT in the encoding phase, possibly due to extraneous activation of the default mode network. By Session 3, participants had learned the LDT and anodal stimulation enhanced retrieval of task information. The attentional spotlight hypothesis was also partially supported, with stimulation disproportionately affecting words with altered spatial properties. This study provides experimental support for this hypothesis and sheds light on the rPPC’s role in learning.
Keywords:
reading,
transcranial direct current stimulation (tDCS),
Posterior parietal cortex,
dorsal pathway,
spatial attention
Conference:
Australasian Society for Psychophysiology, Inc, Coffs Harbour, Australia, 26 Nov - 28 Nov, 2014.
Presentation Type:
Oral Presentation
Topic:
Psychophysiology
Citation:
Bairnsfather
J and
Pammer
K
(2014). Reading and the Posterior Parietal Cortex: A tDCS Study.
Conference Abstract:
Australasian Society for Psychophysiology, Inc.
doi: 10.3389/conf.fnhum.2014.216.00020
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Received:
15 Oct 2014;
Published Online:
02 Dec 2014.
*
Correspondence:
Ms. Jane Bairnsfather, Australian National University, Canberra, Australia, jane.bairnsfather@gmail.com
Dr. Kristen Pammer, Australian National University, Canberra, Australia, kristen.pammer@anu.edu.au